“…8,9 The high yield of 2-cyclopentylidenemethyl-3-hydroxy-1,4-naphthoquinone (4m, 94%) was obtained by the use of β-alanine/acetic acid in benzene under reflux, using only two equivalent excess of aldehyde, compared with five equivalent or higher used by Hooker. 4 Dehydropyranonaphthoquinones (6) could also be obtained using modified Knoevenagel procedure by one-pot condensation-cycloaddition using α,β-unsaturated aldehydes in the presence of ethylenediamine diacetate in moderate to good yields. 10 Anufriev et al, 11 in 1993, using a modified Hooker's methodology with methylamine hydrochloride in ethanol under reflux synthesized 3-alkenyl-2,5,8-trihydroxy-1,4-naphthoquinones (8) besides 3,3'-methylenebisnaphthazarine (9) from naphthopurpurin (7, Table 2). Using few aliphatic aldehydes (propionaldehyde, isobutyraldehyde and valeraldehyde), they observed mixtures of 8 and 9 and using acetaldehyde or paraformaldehyde just dimers were formed.…”